Conventional municipal water treatment (MWT) and other types of water purification systems include multi-stage filtration and sequential process steps for coagulation, flocculation, and sedimentation. A minimum of two stages of filtration typically include coarse 2-3 mm mesh filters at the inlet and 20-40 μm multi-media filters for finishing, although many utilities have more intermediate filtration steps. Neutrally buoyant particles (e.g. particles having substantially the same density as water) can only be filtered or electro-chemically modified for sedimentation. Separation of these types of particles from water is very difficult. Moreover, such particles are typically TOC (total organic carbon) and contribute to major turbidity problems.
A spiral fluidic device useful for membrane-free filtration and separation was described in U.S. application Ser. No. 11/606,460, filed Nov. 30, 2006, entitled “Particle Separation and Concentration System,” which is incorporated herein by this reference in its entirely. In general, such devices are very useful in connection with particles having density differences compared with water, thus creating centrifugal or buoyancy forces necessary for transverse migration through the channel for purposes of separation. However, neutrally buoyant particles present a special case and thus require additional fluidic considerations for separation. Heretofore, such additional considerations have not been fully explored.